Gaining less weight than is recommended was associated with better outcomes among those with prepregnancy BMIs above 40kg/m².

A 2009 guideline from the US Institute of Medicine (renamed National Academy of Medicine in 2015) recommends gestational weight gain of 5 to 9.1 kg for pregnant people with obesity (i.e. body mass index [BMI], 30kg/m² or higher). The safety of less gestational weight gain is unknown. Researchers identified about 16,000 singleton pregnancies affected by obesity (measured before 14 weeks’ gestation) in a Swedish population-based dataset to study the association between total pregnancy weight gain and a composite of neonatal and maternal outcomes. The outcomes, which were weighted for severity, included stillbirth, infant death, large or small for gestational age at birth, preterm birth, unplanned caesarean delivery, gestational diabetes, preeclampsia, excess postpartum weight retention and new-onset chronic maternal cardiometabolic disease. Median follow up was eight years.

Key results were as follows:

• most women (51%) gained more than Institute of Medicine maximum
• recommendations (i.e. more than 9.1kg), 17% gained less than recommended (i.e. less than 5kg) and weight loss occurred in 5%
• weight gain below 5 kg was not associated with risk for the composite outcome among women with class 1 and 2 obesity (BMIs, 30 to 39.9kg/m²)
• weight gain below 5kg and weight loss were associated with lower risk for the composite outcome, compared with recommended weight gain, in women with class 3 obesity (BMIs, 40kg/m² or higher; rate ratio, 0.81).

Comment: These results challenge conventional wisdom (and guidelines) on weight gain in pregnancy. Particularly for women with class 3 obesity, the results support minimising pregnancy weight gain – as long as nutritional balance is maintained. Counselling carefully on healthy pregnancy nutrition at prenatal visits, considering referral for enhanced supports for those with obesity and addressing barriers to accessing healthful food might help optimise outcomes for pregnancies affected by obesity.

Marie Claire O’Dwyer, MB BCh BAO, MPH, Clinical Assistant Professor in Family Medicine, University of Michigan Medical School, Ann Arbor, USA.

Johansson K, et al. Safety of low weight gain or weight loss in pregnancies with class 1, 2, and 3 obesity: a population-based cohort study. Lancet 2024; 403: 1472-1481.

This summary is taken from the following Journal Watch titles: General Medicine, Ambulatory Medicine, Women’s Health.